The effects of a thermally cooled pulsed Nd:YAG laser on the permeabil
ity and structural appearance of the root canal wall were investigated
in vitro. Twenty specimens of freshly extracted human teeth were prep
ared by conventional methods. The teeth were randomly divided into two
groups. Group 1 teeth were prepared conventionally but not lased. Gro
up 2 specimens received three 15-s laser exposures totaling 45 s durat
ion within the root canal via optical fiber delivery. Laser parameters
were set at 5 W, 50 Hz, using a simultaneous air/water coolant spray
of 10 psi air and 2 psi water. The external surfaces of the teeth were
sealed with acrylic and placed in 2% methylene blue dye for 24 h. The
teeth were then sectioned, photographed, and compared under light mic
roscope for the extent of dye penetration. The specimens were subseque
ntly prepared for scanning electron microscopy for correlation of perm
eability measurements with surface modifications. The combined use of
scanning electron microscopy and dye permeability measurements reveale
d a sealing of the dentinal wall by deposition of glass-like material
and, in one specimen, the bridging of a lateral canal that partially o
ccluded the canal. Based on statistical comparisons, permeability of l
aser-treated teeth was significantly less than untreated specimens (al
pha = 0.005).